The present invention relates to an electronic control system for an internal combsution engine, and more particularly to an improvement of such an electronic control system as disclosed in copending U.S. Pat. application filed on Aug. 8, 1979 for controlling air-to-fuel ratio of the mixture supplied into an intake manifold of the engine in relation of the quantity of exhaust gases recirculated into the intake manifold from an exhaust pipe of the engine.
To ensure optimum operation of an internal combustion engine, the inventors have examined an interrelationship between functions of a carburetor and an exhaust gas recirculation system adapted to the engine. As a result, the inventors have found the fact that it is necessary to decrease air-to-fuel ratio of the mixture in accordance with increase of the quantity of recirculated exhaust gases and to increase air-to-fuel ratio of the mixture in accordance with decrease of the quantity of recirculated exhaust gases.